1. Field of the Invention
The invention relates to anhydrous cosmetic stick formulations such as lip balms, lipsticks, and underarm deodorant or antiperspirant sticks, comprising an organic matrix having particles homogeneously dispersed therein, which particles are preferably prepared by a process comprising spray-drying a mixture of liposome encapsulated active agent, modified starch, and optionally maltodextrin.
2. Description of the Related Art
Application of a topical biological active agent directly to skin results in an initial burst of activity. However, this activity phases out quickly. Accordingly, to prolong or delay activity, the active agent must be formulated into a product which gradually releases active agent. It is even more preferred to formulate the product in such a manner that the active agent is released precisely at the time of greatest need. Consumers expect a high level of sophistication in their products. There is thus a need for an intelligent skin care product which can provide not only prolonged release of active agent, but which also coordinates peak delivery of active agent to a particular biological demand. This responsive delivery is referred to herein as controlled delivery.
In recent years increasing attention has been paid to the development of liposomes for use as microscopic "containers". Liposomes have been used to deliver active agent to the skin. For example, U.S. Pat. No. 5,128,139 (Brown et al.) teaches a deodorant comprising liposomes containing grapefruit seed extract. The bioactive agents are entrapped within multilamellar liposomes complexes to provide release over time. Brown et al. acknowledge that liposomes are inherently unstable and tend to break apart, releasing the contents within. Brown et al. thus layers the liposomes or forms them into clusters such that the liposomes which are confined within or are sandwiched between outer layers of liposomes are protected and are more likely to remain stable, while the outer "sacrificial" liposomes tend to break apart releasing their contents during product formulation. This premature release of liposome content is undesirable where the liposome content is a high-value or potent active agent. Further, this formulation does not provide controlled release, i.e., coordination of release in response to biologic demand.
U.S. Pat. No. 4,937,078 to Mezie et. al. discloses the incorporation of topical anesthetic active agents into liposomes which essentially encapsulate the active ingredient within layers of lipid material. It is reported that these lipid vesicles provide a more pronounced cutaneous anesthetic or analgesic effect while employing less of the topical anesthetic agent. The lipid vesicles allegedly provide a means of prolonging the permeation rate without the risk for discomfort due to numbness or systemic reactions. However, prolonging release simply refers to constant rate of release over an extended period of time. There is no mention of suppressing active agent until triggered by a biologic need, then releasing an amount of active agent commensurate with the need.
U.S. Pat. No. 5,510,120 (Jones, et al.) teaches a cosmetic composition for topical application to the skin and/or hair. The composition comprises microcapsules or liposomes which enclose a cosmetically-effective benefit agent (e.g., an agent intended to modify or enhance body odor) active at a target location accessible by application to the skin and/or hair. The particles have means, namely lectin, for binding to targeted microorganisms present on the skin and/or hair, for example those bacteria responsible for skin disorders, scalp irritation, and underarm and foot odor. The encapsulated active agent may be used in combination with a vehicle or carrier such as water, various liquid substances, and various powders such as chalk, talc, fullers earth, kaolin, starch, gums, colloidal silica, etc. While Jones et al. teach targeting delivery of active agent in terms of location, they do little to target delivery in terms of time, i.e., controlling release to peak at the time of greatest need.
U.S. Pat. No. 5,783,211 (Manzo et al) describe the production of starch based particles which encapsulate active agents such as pharmaceutical or cosmetic active ingredients and provide controlled release these active agents. The material produced according to this patent is a powdery cosmetic formulation, e.g., baby powder. As the starch absorbs moisture, the liposomes disintegrate resulting in the release of the active agent. The particles thus provide controlled release of the encapsulated active agent precisely at the time of need. Unfortunately, dry powder formulations are not suitable for use by most adults, since fine white powders do not remain on the skin and tend to migrate through clothes and show up particularly on the outside surface of dark clothes.
It would thus be of interest to be able to adapt the moisture triggered controlled release system of U.S. Pat. No. 5,783,211 to other cosmetic applications. However, liposomes are delicate, and it would be expected that active-agent containing liposomes would be destroyed during the process of formulating cosmetic stick products. Further, it would be expected that waxes and oleophilic organic ingredients of stick formulations would mask the liposomes, and interfere with the controlled release of active substance in response to biological demand.
Accordingly, there remains a need for a new type of delivery system which satisfies a number of requirements, namely, it must be capable of formulating even labile compounds, it must provide enhanced stability, it must be aesthetically pleasing, it must increase efficacy, and it must have reduced irritancy, it must remain in place, and most importantly, it must remain capable of releasing active ingredient in response to biological demand.